The present invention relates to a control device and a controlling method of an inverter that outputs a sinusoidal AC voltage supplied to a motor, by pulse width modulating (PWM) output of a DC power source, and more specifically, the present invention relates to a technique for preventing occurrence of drawbacks caused by a carrier wave, without deteriorating motor efficiency.
There is conventionally known a control device that detects current values of respective phases of a U phase, a V phase, and a W phase of a 3-phase brushless DC motor (hereinafter, “motor”), and PID (proportion/integration/differentiation) controls detected values and generates PID control values so as to follow a sinusoidal current command value, and switches on/off of a switching element structuring an inverter according to a relationship of magnitudes between the PID control values and a triangular wave-shaped carrier wave (hereinafter, “carrier wave”) in order to modulate the PID control values. According to such a control device, it is possible to carry out feedback control so that sinusoidal currents flow at the respective phases of the U phase, the V phase, and the W phase of the motor.
Such an inverter is generally called a triangular wave comparing type sine wave PWM inverter. It is known that, as a switching operation is carried out, this triangular wave comparing type sine wave PWM inverter generates drawbacks due to a frequency of the carrier wave, such as mechanical/electrical vibrations, noise, sound, EMI (ElectroMagnetic Interference), and the like. Therefore, as disclosed in Japanese Patent Application Laid-Open No. 2000-184729, in order to decrease mechanical/electrical vibrations due to the frequency of the carrier wave in conventional control devices, a peak value of a spectrum is kept low by randomly switching the frequency of the carrier wave and diffusing the spectrum of the carrier wave.